Low emf compact duct spacer

ABSTRACT

Conduit spacers useful in preparing duct banks with reduced electromagnetic fields (EMF) are disclosed. The conduit spacers are designed to maximize phase cancellation of EMF from a closely-spaced series of electric power cables placed in conduits supported underground by the conduit spacers. The spacers are also designed to minimize the EMF above ground by reducing the distance needed to bury the cables for a given EMF above ground. In one embodiment, the spacers place conduits adjacent one another for maximum cancellation of a single three-phase cable installation. In another embodiment, the spacers place conduits adjacent one another for maximum cancellation for a dual three-phase cable installation, including cross-phase cancellation, e.g., A-B-C and C-B-A.

TECHNICAL FIELD

This application is a divisional application of U.S. patent applicationSer. No. 13/869,676, filed Apr. 24, 2013, now U.S. Pat. No. ______, andwhich is hereby incorporated by reference in its entirety. U.S. patentapplication Ser. No. 13/869,676 claims priority to, and the benefit of,U.S. Non-provisional application Ser. No. 61/678,946, filed 2 Aug. 2012,which is also hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The technical field is that of methods and apparatus for separating andsupporting power and communication conduits in underground trenches inorder to minimize electromagnetic field emissions.

BACKGROUND

Electric-power transmission is the bulk transfer of electrical energyfrom generating power plants to electrical substations. Mosttransmission lines use high-voltage three-phase alternating current (AC)that requires three conductors (three cables). Three-phase alternatingcurrent (AC) is used because it can be transmitted at high voltages (110kV or above) or extra high voltage (230 kV to 765 kV) to reduce theenergy lost in long-distance transmission. Using transformers, theelectricity can then be efficiently reduced to sub-transmission level(33 kV to 132 kV) and distribution level (3.3 kV to 25 kV). Finally, theenergy is transformed to low voltage (240V or 440V) for use in homes andsmall business. Due to the evolution of power systems, the transmissionvoltages, sub-transmission voltages, and distribution voltage rangesoverlap somewhat.

Transmission lines may be supported by poles or structures and runoverhead or to a lesser degree may be run underground. Some power linesare directly buried in the ground but, as a standard practice, missioncritical underground transmission lines are placed in duct banks. Theduct banks are normally at least three feet below ground level andconsist of multiple conduits that are located a controlled distanceapart in an organized matrix that is encased in concrete. In thisdisclosure, the words duct, conduit and pipe are interchangeable andhave the same meaning. In addition, the word concrete is usedinterchangeably with thermal concrete, concrete slurry or flowable fill.These materials are used to separate the conduits and conduct heat awayfrom the conduits.

The power cables are placed in concrete-encased duct banks for severalreasons. The concrete protects them, primarily from digging, whetherwith hand tools or with mechanized equipment, such as backhoes.Backfill, roads, railroads and the like are placed on top of the ductbank, resulting in heavy loads on the duct bank. A duct bank backfillmaterial other than concrete may settle unevenly. As the concretesettles, the conduits within the concrete matrix settle in unison. Thebase spacers in the duct bank are supported by undisturbed earth andresist movement of the settling conduits. Irregular movement caused bysettling would otherwise deform or crush the conduits. The encasedconduits, arranged in their current volume of usage, are made from PVC,HDPE or FRE (fiberglass-reinforced epoxy). Other conduit materials areused to a much lesser degree. The concrete also acts to dissipate theheat generated by transmission of electric power through the cables.

A typical method that is used to construct an underground powertransmission line is as follows:

-   -   1. Open cut a trench to the required width, depth and length.    -   2. If required, reinforce or shore up the walls of the trench to        insure that it doesn't cave in during the duct bank installation        process.    -   3. Build the duct bank.        -   a. Place base spacers on the bottom of the trench.        -   b. Top load a row of conduits into the base spacers.        -   c. Solvent cement the row of conduits to the previously laid            section of duct bank.        -   d. Place an intermediate row of spacers atop the previously            laid row of duct spacers or conduits.        -   e. Top load the next row of conduits into the intermediate            spacers.        -   f. If “e” was the top row of conduits go to “g,” otherwise            go to “d.”        -   g. If desired, place a top row of spacers atop the            previously laid row of duct spacers or conduits. This top            row of spacers can be used to gage the depth of the concrete            cover and aid in the hold down.    -   4. Place a hold down mechanism atop the duct bank. A hold down        mechanism is required to keep the duct bank from floating when        the concrete is poured. An example is to use rebar (reinforcing        rods of steel) to tie the duct bank structure to the floor or        side walls of the trench.    -   5. Pour concrete over the duct bank, completely encasing the        duct bank. Normally there should be 3 inches of concrete between        the bottom of the lower-most conduits and the bottom of the        trench, 3 inches of concrete on each side of the duct bank and 3        inches of concrete cover atop the upper-most row of conduits.    -   6. Allow the concrete to harden.    -   7. Remove the trench side wall shoring and hold down mechanism        as applicable.    -   8. Backfill the exposed trench opening with the appropriate        backfill material. Compact the backfill in lifts as required.    -   9. Mate the ends of the duct bank with manholes or vaults that        have normally already been put in place.    -   10. Pull the cables down through the manholes or vaults and        through the conduits.    -   11. Restore the surface above the backfill and around the        manholes or vaults as required.

Most overhead and underground transmission lines consist of two sets ofthree cables (six cables). The double set of cables allows for thererouting of power through the backup cable set in the event of anemergency situation. For underground duct banks the cable sets may besituated one atop the other or side by side depending on the width ofthe real estate available and the obstructions encountered along thelength of the duct bank.

An electro-magnetic field (EMF) emanates from electric current beingtransmitted by power cables. Extensive studies have been made on howarrangement of the cables affects EMF from the cables. Electric PowerHigh-Voltage Transmission Lines: Design Options, Cost and Electric andMagnetic Field Levels, J. B. Stoffel, E. D. Pentecost, R. D. Roman andP. A. Traczyk, Environmental Assessment Division, Argonne NationalLaboratory, ANL/EAD/TM-31, November 1994 (hereinafter “Stoffel”). TheEMF is strongest close to the cables and diminishes as the distance fromthe cable increases. The highest EMF levels for an undergroundtransmission line are directly above the transmission line duringmaximum current flow. The higher the current flow, of course, the higherthe EMF. The study found that placing power lines in a triangular ordelta configuration and placing cables closer together led to anapparent cancellation effect and a lower EMF. The study considered a 345kV line with phases spaced 8 inches (approx. 20 cm) apart and buried ina steel pipe 5 ft (approx. 1.5 m) below the surface. The study reportedthat electric fields were eliminated in underground cables and thatmagnetic fields very much reduced at all points except directly abovethe cable. Previous work found a 94% reduction in magnetic fieldstrength if the conduits were encased in a steel pipe. Stoffel, citingCost Effectiveness Analysis: Mitigation of Electromagnetic Fields,” fromCommonwealth Associates, Inc., 1992.

Some studies have found statistical correlations between variousdiseases and living or working near power lines. In a residentialsetting, there is limited evidence of carcinogenicity in humans. Somestatistical studies have reported that incidents of childhood leukemiaand miscarriages increase when the average exposure to a residentialpower-frequency magnetic field is above 3 mG (milliGauss) to 4 mG. See,e.g., A Pooled Analysis of Magnetic Fields and Childhood Leukaemia, A.Ahlbom et al., Br. J. Cancer 200; 83:692-8, cited in Childhood Cancer inRelation to Distance from High Voltage Power Lines in England and Wales,G. Draper et al., Br. Med. J., 2005, vol. 330, pp 1290-94. None of thestudies or evidence available to date has conclusively proven thatexposure to an EMF above 3 to 4 mG is detrimental to human health.Nevertheless, many power utilities and jurisdictions are acting on theside of caution and establishing guidelines and standards that require a“low cost-no cost” mitigation of the EMF emanating from new electricpower transmission and distribution lines and installations.

The EMF emanating from power cables may be reduced considerably by phasecancellation using a triangular configuration and reducing the distancebetween the cables. The phase cancellation technique may require usinglarger diameter cables to reduce heat generation. Additional EMFreduction may be gained from cross-phase placing of the cables of thesix-cable configuration. Stoffel, pp. 16-19, 21-23 and 30.

What is needed is better conduit spacing and a better conduit spacer tominimize electromagnetic emissions from underground cables. The presentdisclosure includes discussions of systems and methods to minimize theseemissions in an economical manner.

BRIEF SUMMARY

One embodiment is a conduit spacer. The conduit spacer includes a lowerhorizontal base and three bodies supported above the lower horizontalbase, each body having an opening adapted to support a conduit or pipe,wherein centers of the three conduits or pipes approximate anequilateral triangle with a base in a nominally vertical direction.

Another embodiment is a conduit spacer. The conduit spacer includes alower portion including a horizontal base and at least two conduitsupport bodies supported above the base, each conduit support bodyhaving an open end extending away from said base. The conduit spaceralso includes an upper portion including two conduit support bodieshaving open ends extending downwards and at least one conduit supportbody having an open end extending upwards, wherein the at least twoconduit support bodies having open ends extending away from said baseand the at least one conduit support body having an open end extendingupwards are adapted to support three conduits or pipes, wherein centersof the three conduits or pipes approximate an equilateral triangle witha base in a nominally vertical direction.

Another embodiment is a conduit spacer. The conduit spacer includes alower portion made from plastic material and including a base and twosupport bodies above the base, the support bodies having open endsextending upwards away from said base; and an upper portion made fromplastic material and including two support bodies having open endsextending downwards and at least one support body having an open endextending upwards, wherein three of the support bodies having open endsextending upwards are adapted to support three conduits or pipes havinga same diameter, and wherein centers of the three conduits or pipes forman equilateral triangle with a base in a vertical direction, the base inthe vertical direction defined by centers of the conduits or pipessupported by the at least one support body and one of the two supportbodies above the base having open ends extending upwards away from saidbase, and wherein the other of the two support bodies above the basehaving an open end extending above the base is adapted to support aconduit or pipe having a diameter smaller than the same diameter.

Another embodiment is a conduit spacer. The conduit spacer includes aspacer body comprising a set of three orifices in a configuration of anequilateral triangle having one side perpendicular to a bottom of atrench, wherein the spacer body is adapted for placement into the trenchfor supporting conduits for power cables.

Yet another embodiment is a method for spacing electrical power cables.The method includes steps of arranging a first electrical power cable ina first plastic duct spacer; and arranging second and third electricalpower cables in a second plastic duct spacer, wherein the second powercable is directly above or below the first power cable, and centers ofthe three cables approximate an equilateral triangle having a verticalbase formed by the centers of the first and second cables.

Another embodiment is a method for spacing electrical power cables. Themethod includes steps of arranging a first electrical cable into atleast one plastic duct spacer; and arranging second and third electricalcables into the at least one plastic duct spacer, wherein the secondcable is directly above or below the first cable, and centers of thethree cables approximate an equilateral triangle having a vertical baseformed by the centers of the first and second cables.

Other embodiments and advantages of the invention will become moreapparent from the following detailed description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification illustrate several aspects of the present invention and,together with the description, serve to explain the principles of theinvention. The drawings are meant to be illustrative rather thanlimiting. In the drawings:

FIG. 1 is a perspective view of a duct bank using conduit duct spacersto separate the conduits of dual 3-phase power lines in a triangulararrangement;

FIG. 2 is an elevation view of the embodiment of FIG. 1;

FIG. 3 is a perspective view of a duct bank using duct spacers toseparate the conduits of 3-phase power lines in a triangulararrangement;

FIG. 4 is an elevation view of the embodiment of FIG. 3;

FIG. 5 is a perspective view of a duct bank using duct spacers toseparate the conduits of two side-by-side dual 3-phase power lines in atriangular arrangement;

FIG. 6 is an elevation view of the embodiment of FIG. 5;

FIG. 7 is a perspective view of a duct bank using duct spacers toseparate the conduits of two side-by-side 3-phase power lines in atriangular arrangement;

FIG. 8 is an elevation view of the embodiment of FIG. 7;

FIG. 9 is a perspective view of a duct bank using a single duct spacerto separate the conduits of dual 3-phase power lines in a triangulararrangement;

FIG. 10 is an elevation view of the embodiment of FIG. 9;

FIG. 11 is a perspective view of a duct bank using a single duct spacerto separate the conduits for a 3-phase power line in a triangulararrangement;

FIG. 12 is an elevation view of the embodiment of FIG. 11;

FIGS. 13 and 14 are front and rear perspective views of a first level orbottom spacer for separating conduits for power or communication cables;

FIGS. 15 and 16 are front and rear perspective view of a level 2intermediate spacer for separating conduits for power and communicationcables;

FIGS. 17 and 18 are front and rear perspective views of a level 3intermediate spacer for separating conduits for power or communicationcables;

FIGS. 19 and 20 are front and rear perspective views of a top levelspacer for separating conduits for power or communication cables;

FIGS. 21-24 depict detailed view of a process for insertion of a conduitinto a spacer; and

FIG. 25 is a chart depicting EMF reduction using triangular spacing ofconduits for 3-phase power transmission lines.

While the invention will be described in connection with certainpreferred embodiments, there is no intent to limit it to thoseembodiments. The intent is to cover all alternatives, modifications andequivalents as included within the spirit and scope of the invention asdefined by the appended claims.

DETAILED DESCRIPTION

The duct spacers disclosed herein are directed to constructing compactunderground duct banks for concrete-encased installations. Theconfiguration that is preferred is a delta or equilateral triangleconfiguration in which a base of the triangle is perpendicular to afloor of the trench into which the duct bank is placed. This arrangementhas the advantage of the phase cancelling effect of the closely-spaceddelta configuration of cables, and also has the advantage of the verycompact duct bank that is formed as low to the bottom of the trench aspossible. The prior art primarily shows conductors arranged in a linearformation (with a horizontal or vertical base) or shows the conductorsarranged as in a right triangle—formed by one or two of the conductorsin a first row or column and the other two or one conductor on anadjacent row or column.

Molded Spacer Series

This disclosure includes generally two types of duct spacers, stackablespacers, such as those depicted in FIGS. 1-8 and 13-24. Single typespacers, less amenable to stacking, are exemplified in FIGS. 9-12. Whilenot restricted by the type of process used to manufacture them, thestackable spacers are typically referred to as molded spacers.Single-type spacers, also not restricted by type of manufacture, may bereferred to as fabricated spacers. The duct spacers described herein,especially the stackable-type spacers, may include provisions forsupporting conduit or pipe placed into the spacers. These provisions maybe referred to as a conduit support body having an open end extendingupwards, or extending downwards. The provisions may also be referred toas a generally U-shaped body or an upward or downward facing arcuatebody, or perhaps as a body having an opening adapted to support aconduit or pipe. The opening, in some embodiments, may be in a directionfacing generally upwards or downwards. In its simplest form, the openingcould be an upward or downward facing cradle, or the opening could bedescribed as “an upward or downward depression suitable for positioningand supporting a conduit or conduits.” All of these are intended for useas a conduit support body.

A first embodiment duct bank with the spacers described herein ispresented in the perspective view of FIG. 1. The installation includes aduct bank 2 which has been placed in a trench 3 and then encased inprotective concrete 4. After the concrete cures, the installation isbackfilled with the overburden or earth 5 that was previously removed.Duct bank 2 includes a plurality of large conduits 6 and small conduits7. The conduits are stacked atop each other as shown using duct spacers10, 12, 14, 12 and 10. The duct spacers are staggered horizontally toavoid creation of a vertical shear plane in the concrete. The figuredepicts spacers suitable for a dual 3-phase arrangement 20 of powercables to be placed into the large conduits shown. The smaller conduitsare typically not used for power cable, but may instead be used forfiber optic communications cables, control cables and thermocouples orother temperature elements for monitoring duct bank temperatures. Thesmaller conduits allow options for the utility without increasing thesize or cost of the duct bank. Large conduits 6, 6 a, 6 b and 6 c areidentical; the designations 6 a, 6 b and 6 c, etc., are used todesignate placement or spacing of particular conduits 6 in the figuresthat follow.

Large conduits are “large” compared to the “small” conduits. For examplesmall conduits may be nominally 2-in, 3-in or 4-inch diameter, and largeconduits may be nominally 5-in, 6-inch or 8-diameter. The actual outerdiameters may be, respectively, 2.375 in (60.3 mm), 3.50 in (88.9 mm),4.50 in (114 mm), 5.56 in (141 mm), 6.625 in (168 mm) and 8.625 in (232mm). The top portion of a spacer orifice may be a little smaller thanthe outer conduit dimension, e.g., about ⅛″ (about 3 mm) less indiameter, to allow for a pressure-retention fit of the spacer ears overthe conduits. The embodiments disclosed herein are not limited to thesenominal or actual diameters, but the conduits or cables used may be anysuitable diameters. Coordinate axes for reference are depicted in FIG.1, with axis Z along a width of the spacers or a length of the ductbank, axis X along a front face or length of the spacers, that is, alonga width of the duct bank, and axis Y along a height of the spacers orduct bank.

Duct bank 2 includes a bottom or level one conduit or duct spacer 10,the duct spacer holding a large conduit 6 and a smaller conduit 7. Ductspacer 10 has two upward facing, generally U-shaped members to hold theconduits, as does each of duct spacers 12 and 14. A first level twointermediate spacer 12 is mounted directly above, i.e., stacked andinterlocked by means of the conduits 6, 7, atop bottom conduit spacer10. Conduit spacer 12 sits atop the large conduit and small conduitmounted in conduit spacer 10, with lower portions of conduit or ductspacer 12 mounted directly on the conduits 6, 7. Duct spacer 12 holdstwo large conduits 6 in its upper portions. A third spacer, level threeintermediate spacer 14 sits atop these two large conduits, resting itslower portions on the two large conduits 6. Two additional largeconduits 6 are in turn supported by the upper portions of spacer 14.This arrangement is repeated for a fourth spacer, a second levelintermediate spacer 12, which is inverted. Finally, an inverted bottomspacer 10, acting as a top spacer, sits atop one final large conduit 6and one small conduit 7 in its U-shaped housing portions. Additionallayers may instead be added by using additional intermediate spacersbefore using the top level.

In this figure, each large conduit 6 is portrayed with a power cable 8inside the conduit. Power cables 8 typically each have a centralconductive core 9 a made of many strands of copper or other suitableconductor, and outer insulation 9 b made of non-conductive material. Asis well known to those with skill the art, the outer insulation helps toprotect the conductor inside.

A side or elevation view of the embodiment of FIG. 1 is depicted in FIG.2. The arrangement 20 for dual 3-phase power includes the five spacers10, 12, 14, 12 and 10 arranged in a vertical pattern, with conduits 6, 7as before. In this side view, each large conduit 6 continues to bedepicted with a cable 8 within the conduit. The arrangement is seen toform two vertically aligned columns, a right column 44 with conduits 6a, 6 b and 6 cc, and a left column 42 with conduits 6 aa, 6 bb and 6 c.Spacers 10, 12, 14, 12, and 10 are designed to hold the conduits in thisarrangement, in which half the conduits are aligned vertically in thismanner on the left, and the other half is aligned on the right. Thisview also depicts the slot 128 on the left and tab 127 on the right forspacer 12, as well as tabs 147 on the left and the slots 148 on theright from spacers 14. Inverted spacer 12 is depicted with tab 127 onthe left side of the figure, and slot 128 on the right side. These tabsand slots allow for additional spacers to be joined on the left andright of the pictured spacers.

Note that spacer 10 on the top of this dual 3-phase arrangement is thesame spacer 10 on the bottom, but spacer 10 on the top has been invertedfrom the views shown in FIGS. 13-14. Lower spacer 12 is the same asshown in FIGS. 15-16, but in this case lower spacer 12 is inverted fromthe view shown in FIGS. 15-16.

In this arrangement, the centers of conduits 6 a, 6 b and 6 c form anequilateral triangle 22 (bold-face lines) having a base 24 which isvertical, i.e., perpendicular to the bottom of the trench into which theduct bank is placed. The centers of conduits 6 aa, 6 bb and 6 cc alsoform an equilateral triangle 26 (also bold face lines) with a base 28that is also vertical, perpendicular to the bottom of the trench.Triangle 26 is reversed with respect to triangle 22, i.e., it “points”in the opposite direction, but its base 28 is still perpendicular to thetrench floor. The other sides of triangles 22, 26 are not perpendicularor parallel to the ground. This spacing is achieved with proper designof the spacers in both the horizontal and vertical directions. In orderto preserve the equilateral triangle configuration, the separationbetween the conduits of the triangle should be symmetrical. That is, thelegs of an equilateral triangle all have the same length and the threeangles are equal. To preserve equal length in the legs, the separationfrom the centers of the conduits must be preserved. The verticalseparation between conduits 6 a and 6 b is taken along a line betweenthe centers of conduits 6 a and 6 b. In the same manner, the separationbetween conduits 6 a and 6 c is also taken along a line between theircenters, as is the separation between conduits 6 b and 6 c. Thisseparation is effected by the design of the duct spacers and theplacement of the open shape and the upward-facing portions of thespacers. In the embodiment of FIGS. 1-2, a nominal 2.00 inch (5.1 cm)separation is used. Other separation distances may be used.

It will be recognized that when dealing with plane geometry, there areno perfect sides, legs, angles or triangles. Thus, the terms used inthis disclosure are approximate. When a form of an equilateral triangleis described or claimed, it should be understood that the form is onlyan approximation. The prior art of which the assignee is aware primarilydescribes spacers for regular arrangement of conduits in what may bedescribed as rows and columns. Formation of an equilateral triangleconfiguration may be thought of as displacing conduits in adjacentcolumns upward or downward by a distance that is equal to half adiameter of the conduit plus half the spacing between verticallyadjacent conduits. A further adjustment horizontally, bringing thecolumns closer together, brings the centers of appropriate conduitscloser to the desired equilateral triangle configuration. Nevertheless,there are no perfect equilateral triangles, and appropriate tolerancesshould be used when deciding conformance to this form, e.g., ±10 percenton lengths, ±10 degrees on angles. For example, a triangle havingcorners at 65, 65 and 50 degrees would meet the criteria because all theangles are within 10 degrees of the 60 degrees required for angles of anequilateral triangle. In addition, a rounded corner also falls withinthe meaning of the word “corner,” rather than a sharp-edged corner ormeeting of lines or plane surfaces. A triangle with sides of 9.5, 9.5and 11 cm in length would meet the criteria because all sides are within10% of a length of 10. The same tolerances or approximations also applyto terms such as “vertical,” “horizontal,” “perpendicular,” “parallel,”and the like.

As discussed previously, the cables 8 placed into conduits 6 a, 6 b and6 c may be phases A-B-C of a first 3-phase power supply, and the cableplaced into conduits 6 aa, 6 bb and 6 cc may be phases A-B-C of a secondor backup 3-phase power supply. Each “triangular” power supply is thusarranged for phase cancellation. The cables are also arranged, in thisembodiment, in a cross-phase cancellation arrangement, with the leftcolumn 42 having, from top to bottom, an A-B-C phase arrangement and theright column 44 having a C-B-A phase arrangement. It is not necessary toplace the phases this way, but the work cited above from Stoffeldemonstrates the effectiveness of this arrangement in reducing theemitted magnetic field. For underground installations, the electricfield is zero for all practical purposes.

In the elevation view of FIG. 2, the corners of equilateral triangles22, 26 mark the centers of the conduits 6. With all conduits 6 havingthe same diameter and all cables 8 also having the same diameter andplacement, the centers of the cables 8 will also define the sameequilateral triangles. The only difference would be that these triangleswill be moved downwards an inch or two, as can be estimated from thefigure. Thus, even though the conduits are not filled, the cables stilloccupy the same positions relative to one another. The centers of thecables still form an equilateral triangle in both instances. Thesepositions retain the advantages gained by their triangular arrangement,and they also maintain the advantages of their cross-phase positioningin the columns described above.

This arrangement is also advantageous because it allows the most compactarrangement of conduits and consequently cables that is possible. Evenwith optimal phase cancellation, the magnetic field is highest near thecenter of the duct bank. The only way to decrease the field is to bringthe conductors closer together or to bury the duct bank deeper. Forexample, an extra foot of depth can reduce the magnetic field bydisplacing it one foot further from the surface. Of course, deepertrenches cost more because of the extra effort needed to go deeper. Theextra depth also makes it harder to upwardly and outwardly dissipateheat generated by the resistance of the cables. The higher thetemperature, the higher the resistance, thus requiring a larger cable toreduce heat generation; alternatively, the same cables may be used withlower current. The triangular arrangement also helps because theconduits and thus the cables are closer to the bottom of the trench, dueto the more compact placement of the conduits and cables, by means ofthe spacers, into the trench. An additional reduction in EMF attachesfrom closer placement of the conductors to each other. It is estimatedthat movement of the conductors closer to each other by one inch is whathelps make possible the 58% reduction in magnetic field discussed above.

Several of the many possible embodiments are discussed in thisdisclosure. Another example is depicted in FIGS. 3-4, which depictperspective and elevation views of an arrangement 30 for a single3-phase power supply. The situation in FIGS. 3-4 is similar to that ofFIGS. 1-2, with a duct bank 2 designed and constructed for placementinto a trench 3, then first covered with concrete 4 and then anoverburden of earth 5. Arrangement 30 includes a single base conduitspacer 16, a single first level intermediate spacer 12, and an invertedtop spacer 10. Base spacer 16 cradles two large conduits 6 a and 6 cwhile intermediate spacer 12 cradles a large conduit 6 b and a smallconduit 7. Inverted top spacer 10 sits atop conduits 6 b and 7. Largeconduits 6 a, 6 b, 6 c each hold a cable 8, such as the three cables ofa 3-phase power transmission line. Just as in arrangement 20, thespacers 16, 12, 10 are staggered horizontally to avoid creation of ashear plane in the encasing concrete. Spacer 12 is inverted from theview shown in FIGS. 15-16, and spacer 10 is also inverted from the viewsshown in FIGS. 13-14.

The elevation view of FIG. 4 illustrates how the centers of conduits 6a, 6 b, 6 c form an equilateral triangle 32. Triangle 32 represents theclosest possible placement of the cables, consistent with concrete flowand the dissipation of heat generated by the resistance of the cableconductors to the flow of electricity. The base 34 of triangle 32 isvertical, i.e. perpendicular to the bottom of the trench or the ground.Just as in arrangement 20, the other sides of triangle 34 are notperpendicular to the ground. The cable diameter is not the same as theconduit diameter; but so long as the same conduit diameter is used andthe same cable diameter is used, the triangle configuration will bepreserved for maximum magnetic field cancellation.

FIGS. 5-6 depict another embodiment or arrangement 40, which includestwo dual 3-phase arrangements 20, arranged side-by-side. In thisembodiment, there are two sets of spacers 10 a, 12, 14, 12 and 10 b, onthe left, and spacers 10 b, 12, 14, 12 and 10 a on the right, each setdesigned for dual 3-phase power cables. Each set includes six largeconduits 6 and two small conduits 7 arranged in a double-triangleformation. As before, each leftward pointing lower triangle 22 has abase 24 that is perpendicular to the bottom of the trench. Eachrightward-pointing upper triangle 26 has a base 28 that is perpendicularto the bottom of the trench. In this instance, top and bottom spacers 10a, 10 b have been altered to eliminate the center spacer 117 and are nowdesignated as spacers 10 a (no right side spacer) or 10 b (no left sidespacer). If the stacks become wider, the remaining spacer outer spacer117 may also be eliminated. The top-most spacers 10 a, 10 b, 12 and 12are inverted.

As noted previously, spacers 12, 14, 12 each have tabs 127, 147 andslots 128, 148 for joining with other spacers 12, 14, 12, as shown. Thedual stacks 20 are shown in FIG. 6 as joined to each other in the centerby means of mating slots 128, 148 and tabs 127, 147 from the respectivespacers, the center mating slots and tabs un-numbered for clarity. Thisarrangement helps to keep the duct bank very compact and manageable.However, the left and right sides could also be joined by lateralspacers between the left and right sides, e.g., spacers having a widthdifferent from the width of the spacers shown, spacers whose onlyfunction is to separate the duct banks laterally without supportingconduits. Examples are side spacer components 117 of spacers 10 a, 10 b.

Another embodiment of two side-by-side 3-phase transmission lines isdepicted in FIGS. 7-8. In this arrangement 45, two arrangements ofspacers 10 a, 12, 16 b on the left and 10 b, 12 and 16 a on the rightare used to hold and separate the conduits for two side-by-side 3-phasearrangements 30. The same situation for spacing applies as shown in sideview FIG. 8. The centers of conduits 6 a, 6 b, 6 c form an equilateraltriangle as before, with the cables 8 in conduits 6 a, 6 b 6 c forming afirst 3-phase transmission line. The centers of conduits 6 aa, 6 bb, 6cc also form an equilateral triangle as before. The cables in conduits 6aa, Ebb are intended to be A and B phase so that they are adjacent the Cphase in conduit 6 c. While this may not be as effective a cross-phaseas in arrangement 20, a cross-phase benefit may be obtained. Tabs 127and slots 128 may be used to join the spacers 12 as shown. Spacers 10 a,10 b and spacers 16 b, 16 a may be joined by adhesively bonding them, byfasteners, or they may simply be joined as shown as a simple mechanicalconnection.

Fabricated or Specialty Spacers

The above embodiments use a plurality of carefully designed andmanufactured spacers to insure the precise spacing of the conduits, andthus the conductors, for underground power transmission lines. Spacersmay also take the form of a single spacer with orifices placed for thesame desirable low EMF effects discussed above, as seen here in FIGS.9-12. Using a horizontal arrangement of single spacers, a duct bank canbe preassembled in long sections outside the trench and then droppedinto the trench. There is less need for personnel to remain in thetrench except for areas where the long sections are joined to each otheror where the duct bank is joined to a manhole. With little need forpersonnel in the trench, it is typically not necessary to shore thetrench for installer safety; the entire duct bank assembly andinstallation may then be completed in considerably less time. Withfabricated spacers, special provisions for rebar placement and auxiliaryconduits can be added to the router program or other fabrication processwith little difficulty.

FIGS. 9-10, for example, depict the same arrangement 20 of dual 3-phasetransmission lines discussed above, with conduits and cables spaced inan equilateral triangle 22, 26 arrangement with bases 24, 28 roughlyperpendicular to the bottom of trench 3 or the ground. In thisembodiment 50, a single spacer body 50 a is supported by a spacer base50 b on the bottom of a trench 3. In one embodiment, spacer body 50 a isfabricated from 0.5 inch thick HDPE sheet stock using a CNC router.Alternatively, spacer 50 a could be injection molded for a lower cost ifvolume warrants. Spacer body 50 a is joined to spacer base 50 b with aslit 50 c in the base. When the installation is complete, the duct bank2 is encased in concrete 4 and then covered with overburden 5, such aswith earth. Single spacer body 50 a may be any suitable width, such as¼″ to ½″, although embodiments may use widths that are greater ornarrower than these.

Spacer body 50 a may be a sheet of plastic or composite material, and itmay be fabricated by any conventional plastic processing technique, suchas injection molding or compression molding. Extruded sheet stock mayalso be used, i.e., cut into the desired outline of the spacer and thenprovided with orifices as shown by drilling, punching, or othermaterial-removal technique. For example, the spacer body 50 a may havesmall utility orifices 52 for handling and stacking. Orifices 52 mayalso be used to anchor the spacer, and thus the duct bank, to the trenchor ground in which it is to be installed, for example by using rebar orother anchors. Large orifices 54 are intended for the 5-in to 8-inchconduits discussed above, while small orifices 56 are intended for thesmaller 3-4 inch orifices. The small and large size orifices are notlimited by these sizes. The same advantages of close proximity and phasecancellation effects for the conduits apply to single-spacer embodimentsas well. Thus, spacer body 50 a is intended to support conduits for dual3-phase transmission lines, just as the multiple spacers shown in FIGS.1-2 and described above with respect to those figures, including thetriangular spacing, the compact spacing, and the phase cancellationeffects, including cross-phase cancellation effects.

FIGS. 11-12 depict an embodiment in which a single 3-phase transmissionline arrangement 30 is supported by a spacer 60 which includes a spacerbody 60 a and a spacer base 60 b to support spacer body 60 a in thebottom of the trench 3, as shown. Spacer body 60 a is joined to spacerbase 60 b by a slit 60 c in the spacer base. Spacer body 60 a includes 3large orifices 64 for conduits and a single small orifice 66 for asmaller conduit. Utility holes 62 are also provided. The arrangement oflarge orifices 64 provides the same triangular spacing 22, 24 discussedabove for FIGS. 3-4, as well as the same compact spacing and the phasecancellation effects.

The discussion above has focused on the desired arrangements ofconduits. The spacers themselves are now discussed. The first level orbase duct spacer 10 was used in many of the embodiments discussed aboveand is described in FIGS. 13-14. The larger U-shaped body 112 isintended to hold a larger conduit, e.g., 5-8 inch diameter, while thesmaller U-shaped body 113 is intended for a small conduit, e.g., 2-4inch diameter. The spacer includes a base 111, a larger generallyU-shaped body 112, a smaller generally U-shaped body 113, feet 118 andside-spacer components 117 for insuring a proper gap between the spacerand the walls of the trench. In one embodiment, spacers 117 are threeinches (approx. 76 mm) wide, to insure a proper amount of concrete onsides of the duct bank. Feet 118 add stability to the spacers and to theduct bank when the duct bank is assembled inside or outside the trench.In addition, when spacer 10 is inverted and used as a top spacer, asseen in FIGS. 1-6, feet 118 and base 111 are atop the spacer. The feetand base provide an integral and handy concrete gauge when the concretepour is made—when the feet and base or concrete gauges are covered, theconcrete fill is sufficient. This also applies to the feet 168 and base163 of spacer 16, depicted in FIGS. 19-20 below.

The U-shape bodies 112, 113 form an arc, a majority of a circle.U-shaped body 112 includes ears, extensions or upper portions 112 awhile U-shaped body 113 includes ears, extensions or upper portions 113a. In one embodiment, the arc is about 270°, centered on the bottom ofcircular shape. In other embodiments, the arc may be more or less than270°, so long the arc is sufficient to hold the conduits in place. Thisshape also applies to the U-shaped bodies described in spacers 12, 14and 16 below. The upper portions or sides of the arc, the arms, areintended to act as snap-fits when the conduits are inserted into thespacers. These upper portions of arms or U-shaped bodies are alsoapparent in the spacers 12, 14 and 16 of FIGS. 15-20 below. The bodiesneed not be U-shaped, but may be any suitable shape, such as a roundedsquare or other geometry, so long at the body is open to accept aconduit.

The bodies are supported above the base with ribs, including buttress114, full-width ribs 115 and half-width ribs 116. There is also what maybe termed a horizontal rib 119, which acts as an upper support betweenthe two generally U-shaped bodies 112, 113. Rib 119 allows U-shaped body112 to flex when a pipe or conduit is assembled into the spacer. Thespaces on the either side of rib 119 act as reliefs that permit the ribto move downwardly when receiving the pipe or conduit and then to flexback upwardly, at least partially, after assembly. In addition to actingas a base spacer, spacer 10 can function as a gauge for the amount ofconcrete or other filler added to the duct bank. The full width rib 115is about 1.5 inches (about 4 cm) long in one embodiment. If this spaceris installed upside-down on the top tiers of conduits, installers knowthey have placed the proper amount of concrete into the trench when thespacer is just covered. The spaces between the top and bottom of spacer10, and spacers 12, 14 and 16, have relatively large open areas andpresent low resistance to the flow of concrete through the spacer. Thislarge open area reduces the possibility of shear planes in the concreteduct back.

Spacer 10 differs from the other spacers depicted below in that spacer10 does not have tabs and slots on its sides for horizontal joining withother spacers 10. As shown in FIGS. 6 and 8 above, horizontal joining ofduct banks may be accomplished by using the tabs and slots of the otherspacers and if necessary, by using adhesive bonds or fasteners on theselower lever spacers. The joining may be aided by removing side spacecomponent 117 or 167 on the appropriate side, as shown in FIGS. 5-8above. In one embodiment, the spacers 10, 12, 14 16 are designed so thatspacers 10 and 16 “fit” horizontally as shown in FIGS. 5-8 with joinedspacers 10 and 16, using the tabs and slots of spacers 12, 14. In thisdescription, spacer 10 is designated as spacer 10 a or 10 b when one ofthe side space components has been removed, e.g., cut off, and spacer 16is designated as spacer 16 a or 16 b when one of the side spacecomponents has been removed.

The second level intermediate spacer 12 is depicted in detail in FIGS.15-16. This spacer is intended for use in an upside-down orientation tosit upon the conduits placed into the base spacer 10, and is alsodesigned to hold and support two large conduits. Spacer 12 includes asmaller upward-facing generally U-shaped body 123 with extensions 123 afor placement atop the smaller conduit placed into spacer 10 and alarger upward-facing generally U-shaped body 124 with extensions 124 afor placement atop the larger conduit placed into spacer 10. Inner andouter supports 131, 132 help to retain dimensional integrity betweenU-shaped bodies 123, 124 and to help support the conduits when placedtherein. The spaces on the either side of rib 131 act as reliefs thatpermit the rib to move downwardly when the spacer is receiving the pipeor conduit and then to flex back upwardly, at least partially, afterassembly. Spacer 12 also includes a first downward-facing arcuate body121 with extensions 121 a for accommodating a larger conduit placedtherein, a second downward-facing arcuate body 122 with extensions 122a, also for accommodating a second larger conduit placed therein, andinner support 129 between U-shaped bodies 121, 122, with space 130between support 129 and U-shaped body 121. The arcuate bodies 121, 122each form an arc, a shape in the form of a partial circle, in thisembodiment about 270°. Other embodiments may have different amounts ofcoverage, so long as the opening or arc is sufficient to provide supportfor the spacer above the conduits on which the spacer rests, and so longas the spacer is able to provide support for the conduits to be placedinto the spacer. This description also applies to the down-ward facingarcuate bodies in spacers 14 and 16 below. While the several bodies ofthe spacer are described as “arcuate,” they may be any suitable opengeometry, such as an open rounded polygon, square, pentagon, and soforth.

A series of full-width ribs 125 and half-width ribs 126 provides supportbetween the upper and lower portions. Spacer 12 also has tapered tabs127 and slots 128 for joining adjacent spacers. As better seen in FIG.16, tabs 127 are tapered in the direction shown, with the back having alarger diameter tapering to a smaller diameter in the front. Slots 128are also tapered in the same direction. The downward-facing generallyU-shaped bodies 121, 122 are spaced for the proper separation,horizontal and vertical, so that when conduits are placed into them, thecenters of the conduits form an equilateral triangle. That is, conduitsplaced into U-shaped bodies 122 and 124 will be vertically aligned.Centers of conduits placed into U-shaped bodies 121, 122 and 124 willform an equilateral triangle.

Third level intermediate spacer 14 is described in detail in FIGS.17-18. Spacer 14 includes a lower upward-facing generally U-shaped body141 and an upper generally U-shaped body 142. The spacer also includes alower downward-facing arcuate body 143 under U-shaped body 141 and anupper downward facing arcuate body 144 under U-shaped body 142. Thegenerally U-shaped bodies 141, 142, 143, 144 also include ears orextensions 141 a, 142 a, 143 a and 144 a which assist the U-shapedbodies in retaining the conduits fit into the spacers. The U-shapedbodies are joined to the arcuate bodies by full width ribs 145 andhalf-width ribs 146, along with support ribs 149 between the upper andlower support bodies. The spaces on the either side of rib 149 act asreliefs that permit the rib to move downwardly when U-shaped body 141 or142 is receiving the pipe or conduit and then to flex back upwardly, atleast partially, after assembly.

Spacer 14 also has tapered tabs 147 and slots 148 for joining adjacentspacers. The upward-facing generally U-shaped bodies 141, 142 are spacedfor the proper separation, horizontal and vertical, so that whenconduits are placed into them, the centers of the conduits form anequilateral triangle. Conduits placed into U-shaped bodies 141 and 142will be vertically aligned with conduits placed into U-shaped bodies 121and 122. As noted, additional levels of conduits may be added to theduct bank by using additional levels of third intermediate spacer 14. Aspreviously, while the bodies of spacer 14 are described as arcuate orU-shaped, any suitable open space or geometry will suffice.

When the desired number of layers is almost reached, level four or toplevel spacer 16 may be used to support the top row of conduits. Detailsof top spacer 16 are shown in FIGS. 19-20. The spacer includes a lowerupward-facing generally U-shaped body 161 with arm extensions 161 a andan upper upward-facing generally U-shaped body 162 with arm extensions162 a, similar to the 270° arc described above for other spacerembodiments. The generally U-shaped bodies are supported laterally byupper support 169. U-shaped bodies 161, 162 are intended for holdinglarge conduits and may be used as a bottom spacer, as shown in FIGS.3-4, or may be inverted and used as a top spacer, as shown in FIGS. 7-8.The U-shaped bodies are joined to the arcuate portions with full-widthribs 165 and half-width ribs 166. Spacer 16 also includes a spacer base163, transverse ribs 164, side spacer components 167 and feet 168. Sidespacer components 167 are typically used to insure a desired minimumwidth of concrete for the finished duct banks. In one embodiment, sidespacer components 167 are about three inches (about 76 mm) wide. Otherdimensions may be used. Spacer 16 is designated as spacer 16 a or 16 bwhen one of the side spacer components is removed, e.g., by cutting offthe spacer. A center of conduits placed into the generally U-shapedbodies 161, 162 are intended to directly align with the U-shaped bodies121, 122 of spacer 12 of spacer 10 to form an equilateral triangle, asshown in FIGS. 3-4 and 7-8.

It has been discovered that the profile of the generally U-shaped bodiesof spacers 10, 12, 14, 16 has an unexpected benefit in assembling ductbanks. Assembly of the spacers into duct banks is discussed withreference to FIGS. 21-24. In FIG. 21 a conduit 6 c is about to be placedinto the lower upward-facing generally U-shaped body 121 of spacer 12.Conduit 7 has already been placed into smaller generally U-shaped body113 of base conduit spacer 10 and conduit 6 a has been placed into thelarger generally U-shaped body 112 of base conduit spacer 10. FIG. 22 isa close-up of the circled area of FIG. 21. The close-up view shows thatupper portion or ear 121 a of the right hand side of U-shaped body 121is in the path of progress of conduit 6 c on its path to installation.Also shown in FIG. 22 is inner support 129 between U-shaped bodies 121,122 and supporting rib 126, a half width rib. In some embodiments,U-shaped bodies 121, 122 provide about 270 degrees of coverage for theconduit. Thus, the upper portions or ears 121 a, 122 a, will have tomove if conduits are to be installed. Note the space or void 130, i.e.,a relief, in the area between ear 121 a and inner support 129.

The needed movement is depicted in FIGS. 23-24. As the conduit islowered, the conduit urges aside ear 121 a as seen in FIG. 23. Thedetail of the movement is depicted in FIG. 24, a close-up of the circledportion of FIG. 23. In FIG. 24, the downward movement of conduit 6 c haspushed aside ear 121 a. This movement is made possible by the flexing ofinner support 129. Movement of ear 121 a and inner support 129considerably reduces the size of the space or void 130, as shown. Ifinner support 129 does not yield, the upper support may be broken orinstallation will not be possible. With this design, upper portions orears 121 a are easily moved aside, and then conduit reaches full depth,the ears 121 a can snap back into place, much as a snap-action orsnap-fit assembly works. This design with moveable ears and flexiblesupports is part of each of spacers 10, 12, 14 and 16.

Present designs call for inner support 129, and the supports for theother spacers, to be full-width supports, extending across the fulldepth of the U-shaped bodies 121, 122 in spacer 12, along coordinateaxis Z in FIGS. 7, 15 and 16. The full depth allows for uniform supportacross the depth of the spacer. The thickness of support 129, as well asthe material used, will then determine its ability to flex and allowentry of the conduit, while retaining sufficient rigidity to providegood support to the conduit in the duct bank. Previous designs includeda tab at about 90° at the terminus of the upper portion or ear 121 a.The tab in earlier designs prevents entry of the conduit while thisdesign allows for easy yet secure assembly of the duct bank.

While FIGS. 9-12 depict useful embodiments, there are many otherembodiments. These fabricated single-body spacers may have tabs andslots, i.e., joining members, for assembly with other spacers in ahorizontal direction. In addition, the single body spacers may becombined with suitable additional slotted supports, horizontal andvertical, to support larger combinations of conduits. In someembodiments, single body spacers may have vertical slots and verticaltabs as well, for assembling multi-tiered banks of spacers for use in amulti-level duct bank. These single-body or fabricated spacers may haveopenings or orifices slightly larger than the expected diameter of thepipe or conduit which is expected to fit within the opening.

In one example, as show in FIGS. 11-12, 8-in nominal conduits have anactual 8.625 in diameter, approx. 21.9 cm, and are separated verticallyby about 2.00 in or 5.1 cm. In addition, spacers for this size conduittypically need to be somewhat larger, e.g., about 8.875 in (22.54 cm) toallow for ease of assembly. For 4-in nominal conduits, the actual outerdiameter is about 4.500 inches and the spacer hole diameter may be about4.750 inches. A first fabricated spacer 60 may have a spacer body 60 aand a spacer base 60 b. The small conduit space is nearest the bottom ofthe trench and has about 3.0 inches (about 7.6 cm) clearance above thebottom of the trench. The center of the conduit orifice is about 5.3inches above the bottom of the trench, with about 3.0 inches forconcrete. The center of the first larger-diameter opening, adjacent thesmall orifice, is about 8.60 inches above the bottom of the trench andincludes about 4.19 inches (about 10.6 cm) clearance for concrete fill.The third large orifice is centered above the first large orifice, withthe center of the third large orifice at about 19.02 inches (about 48.3cm) above the ground and with about two inches (about 5 cm) verticalclearance separating the orifices. The second large diameter orifice islocated adjacent the first and third orifices and centered directlyabove the small diameter orifice. The second large diameter orifice hasabout two inches (about 5 cm) vertical clearance above the smalldiameter orifice, the center of the second diameter orifice at about13.81 inches (about 35 cm) above the trench bottom. Additionalhorizontal conduits may be added in the same manner as shown in FIGS.9-10. Of course, different dimensions and tolerances apply for spacersfor different conduits.

The duct spacers are may be made from composite materials or plasticmaterials. These may include injection molded, compression molded orfabricated spacers. For purposes of this disclosure, plastic means athermoplastic, thermoset, reinforced thermoplastic or reinforcedthermoset material. For example, glass-filled nylon, LDPE or HDPEmaterials may be injection molded to form the spacers described herein.ABS or high-impact polystyrene (HIPS) may be injection molded to formthe spacers. Alternatively, sheet stock of nylon, polyethylene orstyrene materials may be cut and machined to form the spacers. Othersuitable plastic or composite materials may be compression molded toform the spacers described herein.

As noted earlier, significant reductions in EMF may be achieved in3-phase power transmission by placing the conductors near each other ina triangular or delta configuration. The emissions of each phase aresufficiently different that significant self-cancelling effects may beachieved. Studies conducted by Argonne National Laboratoriesdemonstrated the EMF reduction that can be achieved by varying theplacement of the conductors, as discussed above in Stoffel (1994). Thestudy compared magnetic fields resulting from transmission of 230 kVpower at 500 A for different configurations of the three conductors foroverhead transmission lines. A standard vertical construction had amagnetic field of about 79 mG directly beneath the conductors. Atriangular configuration yielded a magnetic field of about 59 mG and adual 3-phase arrangement (dual split phase) using six conductors had amagnetic field of about 34 mG. The triangular configuration thus had areduction of about 26% while the dual split phase had a reduction ofabout 58% directly beneath the lines, with greater comparativereductions at greater distances. The data is presented here in Table 1.

TABLE 1 Magnetic field in mG or % reduction beneath overhead power linesfor 230 kV, 500 A Dual Config- Reduction, Split- Reduction, urationVertical Triangular % phase % Result 79.0 mG 58.6 mG 26% 33.5 mG 58%From Argonne National Labs, Stoffel 1994

Additional studies conducted for the Los Angeles Dept. of Water andPower showed that approximately a 57% reduction in the magnetic fieldabove the ground and closest to the conductors was possible. DraftEnvironmental Impact Report, Los Angeles Dept. of Water and Power,SCH#2009091085, City Clerk Filing #EIR-12-007-WP, March 2012 (“EIR2012”). This phenomenon is seen in FIG. 25 for 230 kV 3-phase power, forboth 751 amps (loading not exceeded 95 percent of the time) and 187 amps(average loading), for underground installations. The reduction at 751amps was from approximately 105 mG (milligauss) at the center of ductbank in a horizontal or side-by-side configuration, to about 45 mG whena triangular or delta configuration was used. This represents about a57% reduction. Similar reductions were seen for 187 amps, fromapproximately 26 mG in a horizontal configuration to about 11 mG for thetriangular configuration, which is also a 57% reduction. The data arepresented in Table II. Readings are taken at about 1 m above the ground.In both the conventional and the triangular configurations, the top ofthe duct bank was about 3 ft (about 1 meter) below grade. In general,phase cancellation effects increase the closer the conductors are placedtogether. The triangular configuration used cables placed about one inchcloser than the conventional spacing between cables.

TABLE II Magnetic field in mG at stated horiz. distance or reduction atstated Amps for 230 kV Configuration 0 ft 25 ft 50 ft 75 ft 100 ftHorizontal 751 A 104.76 9.34 2.5 1.13 0.64 Triangular 751 A 45 5.43 1.490.67 0.38 Horizontal 187 A 26.08 2.33 0.62 0.28 0.16 Triangular 187 A11.21 1.35 0.37 0.17 0.09 Triangular 751 A 57 42 40 41 41 % reductionTriangular 187 A 57 42 40 39 44 % reduction From EIR 2012

The data in Table II may be interpreted several ways, but one useful wayis to compare the configurations to see the reduction in magnetic fieldat horizontal distances from the center of the duct bank. Table II isalso constructed to show the considerable reduction in magnetic fieldfrom the triangular configuration as compared to the standard horizontalconfiguration at all distances from the duct bank.

All references, including publications, patent applications, and patentscited herein are hereby incorporated by reference to the same extent asif each reference were individually and specifically indicated to beincorporated by reference and were set forth in its entirety herein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) is to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments are described herein, including the best modeknown to the inventors for carrying out the invention. Variations ofthose preferred embodiments may become apparent to those of ordinaryskill in the art upon reading the foregoing description. Skilledartisans will use such variations as appropriate, and the inventorsintend for the invention to be practiced otherwise than as specificallydescribed herein. Accordingly, this invention includes all modificationsand equivalents of the subject matter recited in the claims appendedhereto as permitted by applicable law. Moreover, any combination of theabove-described elements in all possible variations thereof isencompassed by the invention unless otherwise indicated herein orotherwise clearly contradicted by context.

What is claimed is:
 1. A method for spacing electrical power cables,comprising: arranging a first electrical power cable in a first plasticduct spacer; and arranging second and third electrical power cables in asecond plastic duct spacer, wherein the second power cable is directlyabove or below the first power cable, and centers of the three cablesapproximate an equilateral triangle having a vertical base formed by thecenters of the first and second cables.
 2. The method of claim 1,wherein the three electrical power cables have a same diameter.
 3. Themethod of claim 1, further comprising arranging two additionalelectrical power cables above the second and third electrical powercables with a third plastic duct spacer.
 4. The method of claim 3,further comprising arranging an additional electrical power cable aboveone of the two additional electrical power cables with a fourth plasticduct spacer, wherein the centers of the three additional cablesapproximate a second equilateral triangle with a base in a verticaldirection.
 5. The method of claim 4, wherein the six power cablescomprise two sets of three-phase electrical power cables and arearranged for cross-phasing in the duct spacers.
 6. A method for spacingelectrical cables, comprising: arranging a first electrical cable intoat least one plastic duct spacer; and arranging second and thirdelectrical cables into the at least one plastic duct spacer, wherein thesecond cable is directly above or below the first cable, and centers ofthe three cables approximate an equilateral triangle having a verticalbase formed by the centers of the first and second cables.
 7. The methodof claim 6, further comprising using a second plastic duct spacer forarranging at least one of the second and third electrical cables.
 8. Themethod of claim 6, wherein the first, second and third cables comprisethree phases for three-phase electrical transmission, and furthercomprising arranging three additional cables in the at least one plasticduct spacer, the three additional cables also comprising three phasesfor three-phase electrical transmission, wherein the six cables arearranged for cross-phase EMF cancellation.
 9. A conduit spacer,comprising: a lower horizontal base and three bodies supported above thelower horizontal base, each body having an opening adapted to support aconduit or pipe, wherein centers of the three conduits or pipesapproximate an equilateral triangle with a base in a nominally verticaldirection; and three additional bodies supported above the three bodies,each body having an opening adapted to support a conduit or pipe,wherein centers of the three additional conduits or pipes approximate anequilateral triangle with a base in a nominally vertical direction. 10.The conduit spacer of claim 9, wherein the equilateral triangle has acorner in a first direction from the base of the equilateral triangleand the second equilateral triangle has a corner in a second directionopposite the first direction.
 11. The conduit spacer of claim 9, furthercomprising an additional body having an opening adapted to support aconduit or pipe, wherein the additional body is adapted for placementabove the body opposite the base of the equilateral triangle of thethree additional bodies.
 12. The conduit spacer of claim 9, wherein thebase further comprises at least one side spacer component for providinga measured space for concrete fill.
 13. The conduit spacer of claim 9,further comprising a reinforcing rib between any two of the threebodies, the reinforcing ribs surrounded by reliefs allowing flexure ofthe bodies when pipe or conduit is assembled into the conduit spacer.14. A conduit spacer, comprising: a lower portion made from plasticmaterial and including a base and two support bodies above the base, thesupport bodies having open ends extending upwards away from said base;and an upper portion made from plastic material and including twosupport bodies having open ends extending downwards and at least onesupport body having an open end extending upwards, wherein three of thesupport bodies having open ends extending upwards are adapted to supportthree conduits or pipes having a same diameter, and wherein centers ofthe three conduits or pipes form an equilateral triangle with a base ina vertical direction, the base in the vertical direction defined bycenters of the conduits or pipes supported by the at least one supportbody and one of the two support bodies above the base having open endsextending upwards away from said base, and wherein the other of the twosupport bodies above the base having an open end extending above thebase is adapted to support a conduit or pipe having a diameter smallerthan the same diameter.
 15. The conduit spacer of claim 14, wherein theupper portion having at least one support body having an open endextending upwards comprises two bodies adapted to support two conduitsor pipes of the same diameter, the two bodies having open ends extendingupwards, and further comprising a second upper portion made from plasticmaterial and comprising two support bodies having open ends extendingdownwards and adapted to support two conduits or pipes of the samediameter, and having two support bodies having open ends extendingupwards.
 16. The conduit spacer of claim 15, wherein the two supportbodies of the second upper portion having open ends extending upwardsare adapted to support two additional conduits or pipes of the samediameter, and further comprising a third upper portion having twosupport bodies having open ends extending downwards and adapted tosupport two conduits or pipes of the same diameter, the third upperportion further comprising two support bodies having open ends extendingupwards of which at least one is adapted to support a conduit or pipe ofthe same diameter, and wherein centers of the three conduits or pipes ofthe same diameter supported by the third upper portion approximate asecond equilateral triangle with a base in a vertical direction.
 17. Theconduit spacer of claim 16, wherein the second equilateral triangleformed with centers of the three pipes or conduits of the third uppersection has a corner in a first direction from the base of the secondequilateral triangle and the equilateral triangle has a corner in asecond direction opposite the first direction.
 18. The conduit spacer ofclaim 14, wherein the other of the upwardly extending bodies of thethird upper portion is adapted to support a conduit or pipe having asmaller diameter than the at least one upwardly extending body adaptedto support a conduit or pipe of the same diameter.
 19. The conduitspacer of claim 14, wherein the arrangement of the lower and upperportions and electrical cables in the upper and lower portions isadapted to minimize electromagnetic interference (EMI) emissions fromelectrical transmission lines supported by the support bodies.
 20. Theconduit spacer of claim 14, wherein the base further comprises at leastone side spacer component for providing a measured space for concretefill on a side of the spacer.